The present invention relates to aqueous ink compositions, particularly to quick-drying type aqueous ink compositions suitable for ink jet printing method.
It has bee the common practice to add, to aqueous ink compositions, a surface active substance in order to (a) improve print quality (including adaptability to paper), (b) improve quick drying property and (c) prevent bleeding between adjacent colors upon multi-color printing.
Since a surface active substance to be added to aqueous ink compositions is required to have high penetration promoting effects into a recording medium and structural characteristic that does not cause defects such as bubbling during printing, a nonionic surfactant is often selected as the surface active substance. Particularly, surfactants such as acetylene alcohol compounds and acetylene glycol compounds have attracted attentions as surfactants capable of satisfying the above-described requirements. Among them, acetylene alcohol compounds have markedly high penetration promoting effects and they are known to provide excellent print quality even with a small addition amount (for example, Japanese Patent Laid-Open No. 139964/1988, Japanese Patent Laid-Open No. 239068/1992).
Acetylene alcohol compound based surfactants having a structure exhibiting stronger hydrophobicity are preferred because of their higher penetration promoting effects. They, however, have low solubility in water so that there may be the case where attention should be given to ejection property and clogging property.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an aqueous ink composition excellent in (a) improvement of ejection stability, (b) improvement of print quality, (c) improvement in fixing property (scratch resistance), (d) reduction in running cost, and (e) improvement of adaptability to paper.
Another object of the present invention is to provide an ink cartridge having the aqueous ink composition contained therein.
Other objects and effects of the invention will become apparent from the following description.
The present inventors have investigated and studied improvement in solubility in water of an acetylene alcohol compound based surfactant of a strong hydrophobic structure (which may be hereinafter referred simply to xe2x80x9chydrophobicxe2x80x9d). As a result, it was found that combined use, in an aqueous ink composition, of a specific acetylene alcohol based surfactant and a surface active substance capable of causing an effective amount of the acetylene alcohol based surfactant to dissolve in water makes it possible: to improve water solubility of the acetylene alcohol based surfactant, leading to improvement in ejection stability and clogging resistance without causing defects such as bubbling; to increase the addition amount of the acetylene alcohol based surfactant, so that improvement in print quality, improvement in adaptability to paper and reduction of a running cost can be attempted; and to improve penetration, thereby improving fixing property (scratch resistance) particularly when a pigment is used as a colorant. The invention has been completed based on the above-described findings.
The above-described objects of the invention have been achieved by providing an aqueous ink composition comprising at least: a colorant; water; 0.005 to 10 wt. %, based on the weight of the ink composition, of an acetylene alcohol compound represented by the following formula (1): 
wherein R1, R2 and R3 each independently represents a hydrogen atom, an alkyl group which may be branched, or an alkylphenyl group; and a surface active substance capable of causing the acetylene alcohol compound of formula (1) to dissolve in water.
1) In a first preferred embodiment of the invention, the surface active substance comprises at least one compound selected from compounds represented by the following formulas (21a), (21b), (21c), (21d), (21e) and (21f): 
xe2x80x83wherein R11to R15 each independently represents a C1-15 alkyl group which may be branched, subscripts n1, m1, h1, k1, j1, a, b and c each independently stands for 1 to 30, and M1 and M2 each independently represents a hydrogen atom, an alkali metal or a base such as ammonium.
2) In a second preferred embodiment of the invention the surface active substance comprises at least one 1,2-alkyldiol compound represented by the following formula (22):
HOxe2x80x94CH2xe2x80x94CH(OH)xe2x80x94R21xe2x80x83xe2x80x83(22)
wherein R21 represents a C1-10 alkyl group.
3) In a third preferred embodiment of the invention, the surface active substance comprises at least one compound selected from the compounds represented by the following formulas (23a) and (23b): 
xe2x80x83wherein R31 represents a C1-15 alkyl group which may be branched, or an alkylphenyl group, and subscripts n3 and m3 each independently stands for 0 to 10.
4) In a fourth preferred embodiment of the invention, the surface active substance comprises at least one compound selected from phosphate ester compounds represented by the following formulas (24a) and (24b): 
xe2x80x83wherein R44, R45, and R46 each independently represents a C8-30 alkyl group which may be branched, or an alkylphenyl group, and subscripts n4, m41 and m42 each independently stands for 1 to 30.
5) In a fifth preferred embodiment of the invention, the surface active substance comprises at least one compound selected from:
highly water-soluble acetylene glycol compounds represented by the following formula (25a): 
xe2x80x83wherein R54, R55, R56 and R57 each independently represents a C1-30 alkyl group which may be branched, or an alkylphenyl group, R51 and R52 each independently represents a hydrogen atom or a methyl group, and subscripts n5 and m5 each stands for an integer of 0 to 30; and
highly water-soluble acetylene alcohol compounds represented by the following formula (25b): 
wherein R58, R59 and R50 each independently represents a hydrogen atom or an alkyl group which may be branched, R53 represents a hydrogen atom or a methyl group, and a subscript h5 stands for an integer of 0 to 30, with the proviso that R58+R59+R50 less than 5.
The present invention also relates to an ink cartridge having an ink container containing any one of the above-described aqueous ink compositions.
Components used for the aqueous ink composition of the invention are described in detail below. The term xe2x80x9caqueous ink compositionxe2x80x9d as used herein means, for black-and-white recording, an aqueous black ink composition, while for color printing, it means a color ink composition, more specifically, an aqueous yellow ink composition, an aqueous magenta ink composition and an aqueous cyan ink composition, and further optionally, an aqueous black ink composition.
To the aqueous ink composition of the invention, a water soluble compound can be further added in order to improve recording stability such as writing properties and ejection properties. Addition of a proper water-soluble compound may impart writing things such as pen with smooth writing properties free of partial thinning and inkjet recording with more stable ejection properties. As such a water soluble compound, organic solvents and water soluble solids ordinarily employed for aqueous ink compositions can be used. Specific examples thereof include low-molecular-weight glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and dipropylene glycol; polyols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, pentaerythritol and glycerin; lower alcohols such as ethanol and propanol; cellosolves such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; carbitols such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone and xcex5-caprolactam; ureas such as urea, thiourea, ethylene urea and 1,3-dimethylimidazolidinone; and saccharides such as maltitol, sorbitol, gluconolactone and maltose.
The addition amount of the aqueous compound is added preferably 1 to 30 wt. %, more preferably 5 to 25 wt. %, based on the whole weight of the aqueous ink composition. Amounts exceeding 30 wt. % make it difficult to adjust the viscosity of the aqueous ink composition to fall within a desired range, which may deteriorate ejection stability. Amounts less than 1 wt. %, on the other hand, may fail to bring about desired effects.
The feature of the aqueous ink composition of the present invention resides in the use of the above-described xe2x80x9cat least one acetylene alcohol compound represented by formula (1)xe2x80x9d and the xe2x80x9csurface active substance capable of causing the acetylene alcohol compound of formula (1) to dissolve in waterxe2x80x9d in combination.
By using the xe2x80x9cacetylene alcohol based surfactant represented by formula (1)xe2x80x9d in combination with the xe2x80x9csurface active substance capable of causing the acetylene alcohol based surfactant to dissolve in waterxe2x80x9d in an aqueous ink composition with a view to improving print quality and quick-drying property and preventing, as much as possible, bleeding between adjacent colors upon multicolor printing, water solubility of the acetylene alcohol based surfactant is enhanced and the penetration property of the aqueous ink composition through a recording medium is improved, thereby obtaining excellent effects in improvement of ejection stability, improvement in print quality, improvement in fixing property (scratch resistance), reduction of a running cost and improvement of adaptability to paper.
As the acetylene alcohol compound represented by formula (1), two or more compounds different in R1, R2 and/or R3 can be used together. Specific examples thereof are shown below in Table 1. Of course, the acetylene alcohol compounds usable in the invention are not limited thereto.
Among the acetylene alcohol compounds of formula (1), preferred are those having a structure of stronger hydrophobicity, that is, those greater in the total number of carbon atoms of R1, R2 and R3, because their penetration promoting effects are high.
The acetylene alcohol compounds of formula (1) having 5 or greater, more preferably 7 or greater, carbon atoms in total of R1, R2 and R3 are preferred.
The total amount of the acetylene alcohol compounds of formula (1) contained in the aqueous ink composition is 0.005 to 10 wt. %, more preferably 0.01 to 5 wt. %.
When the total amount of the acetylene alcohol compounds is less than 0.005 wt. %, the desired penetration effects may be hardly exhibited. Total amounts exceeding 10 wt. %, on the other hand, may make it difficult to adjust the viscosity of the resulting aqueous ink composition within a desired range or may cause defects such as marked deterioration in ejection stability owing to low water solubility.
Next, preferred embodiments of the xe2x80x9csurface active substance capable of causing the acetylene alcohol compound of formula (1) to dissolve in waterxe2x80x9d to be used in the invention is described in more detail.
Specific examples of the compound represented by formula (21a) include polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether; specific examples of the compound represented by formula (21b) include polyoxyethylene oleyl ether and polyoxyethylene lauryl ether; specific examples of the compound represented by formula (21c) include polyoxyethylene oleate ester; specific example of the compound represented by formula (21d) include ammonium polyoxyethylene nonyl phenyl ether sulfate; and specific examples of the compound represented by formula (21e) include sodium polyoxyethylene oleyl ether sulfate. Specific examples of these formulae are however not limited thereto.
Examples of the compound represented by formula (21f) include polyoxyethylene-polyoxypropylene block copolymers. Various compounds different in chain length represented by a, b and/or c can be used.
Specific examples of the 1,2-alkyldiol compound represented by formula (22) include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol and 1,2-octanediol. Of course, the 1,2-alkyldiol compounds usable in the invention are not limited thereto.
Incidentally, 1,2-alkyldiol compounds of formula (22) wherein R represents an alkyl group having 11 or greater carbon atoms has reduced water solubility, which might inhibit the addition thereof in an amount sufficient for obtaining desired effects.
As the compounds of formulas (23a) and (23b), compounds shown in Tables 2 and 3 can be given as specific examples, but the compounds usable in the invention are not limited thereto.
The compounds of formulas (23a) and (23b) each contains, in the molecule thereof, an ethylene oxide group and a propylene oxide group. Various compounds different in chain length represented by n3 and/or m3 can be used.
As specific examples of the phosphate ester compounds represented by formulas (24a) and (24b), compounds shown in Tables 4 and 5 can be given. Of course, the phosphate ester compounds are not limited thereto.
As the phosphate ester compounds of formulas (24a) and (24b), various compounds having, in the molecule thereof, an ethylene oxide group and different in chain length represented by n4, m41 and/or m42 can be used.
As the acetylene glycol compound of formula (25a) having high water solubility, two or more compounds different in any of R54 to R57 can be used simultaneously. As specific examples thereof, compounds as shown in Table 6 can be given, but compounds usable in the invention are not limited thereto.
As the highly water-soluble acetylene alcohol compound of formula (25b), two or more compounds different in any of R58, R59 and R50 can be used simultaneously. As specific examples thereof, compounds as shown in Table 7 can be given, but compounds usable in the invention are not limited thereto.
The total addition amount, in the aqueous ink composition, of xe2x80x9csurface active substance capable of causing an acetylene alcohol compound to dissolve in waterxe2x80x9d to be used in combination with the acetylene alcohol compound having a highly hydrophobic structure in order to enhance its water solubility is desirably an amount that allows substantially the whole amount of the acetylene alcohol compound to be dissolved in the aqueous ink composition, preferably 0.1 to 10 wt. %, more preferably 0.2 to 5 wt. %.
Amounts less than 0.1 wt. % may disturb exhibition of desired effects, that is, effects for causing a necessary amount of the acetylene alcohol compound to dissolve sufficiently, thereby presumably deteriorating ejection stability. Amounts exceeding 10 wt. %, on the other hand, may cause defects such as difficulty in adjusting the viscosity of the aqueous ink composition within a desired range.
In the invention, either a dye or a pigment may be used as the colorant. In aspects of light resistance and water resistance, a pigment is preferred. A combination of a pigment and a dye may also be used.
Use of a pigment as the colorant improves penetration property of the resulting aqueous ink composition, thereby bringing about marked effects of improving fixing property (scratch resistance).
The content of the colorant in the aqueous ink composition is preferably about 0.5 to 25 wt. %, more preferably about 2 to 15 wt. %.
No particular limitation is imposed on the pigment employed and either inorganic pigment or organic pigment can be used. Examples of the inorganic pigment include, in addition to titanium oxide and iron oxide, carbon black prepared in a known manner such as contact process, oil furnace process or thermal process. Examples of the organic pigment include azo pigments such as azo pigment lakes, insoluble azo pigments, azo condensation pigments and azo chelated pigments; phthalocyanine pigments such as copper phthalocyanine pigments and metal-free phthalocyanine pigments; polycyclic condensation pigments such as anthraquinone pigments, perylene pigments, perinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments and quinophthalone pigments; dye lakes such as basic dye lakes and acidic dye lakes; nitro pigment; nitroso pigment; and aniline black.
The pigment has a particle size of preferably 10 xcexcm or less, more preferably 1 xcexcm or less.
Examples of the carbon black to be used for black ink include products of Mitsubishi Chemical such as No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100 and No. 2200B; products of Columbian Chemical such as Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255 and Raven 700; products of Cabot such as Regal 400R, Regal 330R, Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, and Monarch 1400; and products of Degussa such as Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A and Special Black 4.
Examples of the pigment to be used for yellow ink include C.I. Pigment Yellow 1, C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14C, C.I. Pigment Yellow 16, C.I. Pigment Yellow 17, C.I. Pigment Yellow 73, C.I. Pigment Yellow 74, C.I. Pigment Yellow 75, C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. Pigment Yellow 98, C.I. Pigment Yellow 114, C.I. Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 151, and C.I. Pigment Yellow 154.
Examples of the pigment to be used for magenta ink include C.I. Pigment Red 5, C.I. Pigment Red 7, C.I. Pigment Red 12, C.I. Pigment Red 48(Ca), C.I. Pigment Red 48(Mn), C.I. Pigment Red 57(Ca), C.I. Pigment Red 57:1, C.I. Pigment Red 112, C.I. Pigment Red 123, C.I. Pigment Red 168, C.I. Pigment Red 184 and C.I. Pigment Red 202.
Examples of the pigment used for cyan ink include C.I. Pigment Blue 1, C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:34, C.I. Pigment Blue 16, C.I. Pigment Blue 22, C.I. Pigment Blue 60, C.I. Vat Blue 4 and C.I. Vat Blue 60.
In the present invention, it is possible to use a pigment (surface-treated pigment) having a surface treated to bond thereto at least one of: functional groups such as sulfone, carbonyl, carboxyl, hydroxyl and amino; and salts thereof, directly or via a bonding group such as a C1-10 alkylene or a phenylene group, thereby allowing it to be dispersible in water without a dispersant.
In the present invention, the pigment is preferably used in the form of a pigment dispersion obtained by dispersing the pigment in an aqueous medium by an aid of a dispersant. As the dispersant to be used for the preparation of the pigment dispersion, dispersants ordinarily employed for the preparation of a pigment dispersion, for example, polymeric dispersants and surfactants may be used. It is apparent that the surfactant contained in the pigment dispersion will also function as a surfactant for the aqueous ink composition.
Preferred examples of the polymeric dispersant include natural polymers. Specific examples thereof include proteins such as glue, gelatin, casein and albumin; natural rubbers such as gum arabic and tragacanth gum; glucosides such as saponin; alginic acid, and alginic acid derivatives such as propyleneglycol alginate, triethanolamine alginate, and ammonium alginate; and cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose and ethylhydroxy cellulose. Preferred examples of the polymeric dispersant also include synthetic polymers. Specific examples thereof include polyvinyl alcohols, polyvinylpyrrolidones; acrylic resins such as polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, vinyl acetate-acrylate ester copolymers and acrylic acid-acrylate ester copolymers; styrene-acrylic resins such as styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylate ester copolymers, styrene-xcex1-methylstyrene-acrylic acid copolymer, styrene-xcex1-methylstyrene-acrylic acid-acrylate ester copolymers; styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer; and vinyl acetate copolymers such as vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymers, vinyl acetate-maleate ester copolymers, vinyl acetate-crotonic acid copolymer and vinyl acetate-acrylic acid copolymer; and salts thereof.
Of these, copolymers of a monomer having a hydrophobic group and a monomer having a hydrophilic group and polymers of a monomer having both a hydrophobic group and a hydrophilic group in its molecular structure are particularly preferred.
The pigment dispersion to be used in the invention can be prepared, for example, by mixing a pigment, a dispersant, water or a mixture of water and a water-soluble organic solvent, and then dispersing the resulting mixture in a disperser such as beads mill, ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer or pearl mill.
In the present invention, various dyes ordinarily employed for ink jet printing such as direct dyes, acid dyes, food dyes, basic dyes, photo-reactive dyes, disperse dyes, vat dyes, soluble vat dyes and reactive disperse dyes are usable as the dye.
To the aqueous ink composition of the invention, a fixing agent may be added further as needed.
Water-soluble resins may be used as the fixing agent. Specific examples thereof include water soluble rosins, alginic acid derivatives, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, styrene-acrylic acid resin, styrene-acrylic acid-acrylate ester resins, styrene-maleic acid resin, styrene-maleate half ester resin, acrylic acid-acrylate ester resins, isobutylene-maleic acid resin, rosin-modified maleic acid resin, polyvinylpyrrolidone, gum arabic starch, polyallylamine, polyvinylamine and polyethyleneimine.
The aqueous ink composition of the invention may contain other additives, for example, a pH regulator, antiseptic and/or mildewproofing agent. Examples of the pH regulator include various amines such as diethanolamine and triethanolamine, and hydroxides of an alkali metal such as sodium hydroxide, potassium hydroxide and lithium hydroxide.
The aqueous ink composition of the invention has preferably a surface tension at 20xc2x0 C. of 20 to 55 mN/m, more preferably 25 to 45 mN/m.
At surface tension less than 20 mN/m, it may occur a phenomenon that the aqueous ink composition unevenly wets the vicinity of an ejection nozzle and such a phenomenon may deteriorate the ejection stability. Surface tension exceeding 55 mN/m, on the other hand, may disturb exhibition of desired penetration effects.
The aqueous ink composition of the invention is preferably employed as an ink for inkjet recording.
The ink cartridge of the invention is equipped with an ink container to contain the aqueous ink composition. The ink container preferably has a mechanism of generating an appropriate negative pressure relative to the atmospheric pressure so as to prevent leakage of the aqueous ink composition from the ink cartridge by gravity even if the ink container is communicated with the air. Examples of the mechanism generating a negative pressure include a structure equipped with a porous ink absorbing material such as polyurethane and a structure to control the shape of the ink container by mechanical action via spring or the like. Either manner may be employed in the invention.
The present invention will be illustrated in greater detail with reference to the following Examples and Comparative Examples, but the invention should not be construed as being limited thereto.